It is known to be desirable in the paper handling art to provide paper handling apparatus, such as: copiers, inserters, and the like, with mechanisms, known as accumulators, which accumulate a sequence of sheets being processed by the apparatus to form a stack, or accumulation, for further processing. For example, a sequence of sheets might be fed to a printer for printing of predetermined information, and the output of the printer fed to an accumulator where a predetermined number of sheets in the sequence would be accumulated, and the resulting accumulation passed on for further processing, such as folding and insertion into an envelope.
Referring to FIG. 1, an example of a buckle type prior art accumulator 10 as substantially taught by U.S. Pat. No. 5,356,263 is shown. The accumulator 10 includes a feed mechanism 20 including a pair of input rollers 22 and a pair of output rollers 24 for feeding a sheet SI along a first path until the sheet is deflected onto a second path. The feed mechanism 20 continues to drive the sheet SI along the second path until the leading edge LE reaches a selectively activatable accumulating stop 12 which halts the leading edge LE of the sheet S1. The input rollers 22 continue to drive the sheet S1 so that the sheet S1 buckles away from the first path in a direction defined by the deflection of the sheet S1. As the input rollers 22 continue to feed the sheet S1 a loop forms B1 and the sheet S1 unrolls into a receiving space 30, which may be no more than an open area provided in the accumulator, so that as the trailing edge TE of the sheet S1 clears the feeder mechanism 20, the trailing edge TE and a substantial portion of the sheet S1 are displaced into the receiving space 30 and away from the first path as defined by the nip of the input rollers 22. Thus, the sheet S1 may be followed by a next sheet S2 which similarly reaches the stop 12 causing a respective loop B2 to form resulting in the accumulation of the next sheet S2 with the first sheet S1.
Although such accumulators generally work well, some difficulties have been experienced. Generally, the need for a receiving space 30 so as to allow the buckle or loop to form does not lend itself to the placement of a guide in an area 50 of the receiving space 30 adjacent to the feed path located between the input rollers 22 and the output rollers 24. As a result, the lead edge LE of the sheet S1 is not controlled on both sides of the sheet S1 meaning that the sheet S1 must bridge the gap between the nip of the input rollers 22 and the nip of the output rollers 24. Therefore, the lead edge LE is susceptible to wandering off the feed path due to a variety of reasons, such as: paper curl, vibration, air turbulence, and the like. Thus, the likelihood of paper jams is increased because the lead edge LE of the sheet S1 may stall in the area 50 of the receiving space 30 and not properly reach the nip of the output rollers 24 resulting in reduced reliability of the accumulator. This is due to the fact that a portion of the sheet S1 extending out from the nip of the input rollers 22 is cantelevered (supported at only one end) until it reaches the nip of the output rollers 22. Contributing to this problem is a practical requirement that the nip of the input rollers 22 cannot be located too close to the nip of the output rollers 24 because adequate leeway must be provided to allow the loop B1 to form. As a result, the gap between the nip of the input rollers 22 and the nip of the output rollers 24 is greater than what one skilled in the art will normally employ in view of the fact that a guide cannot be placed in area 50.
Thus, there is a need for an improved buckle accumulator that reduces the likelihood of jams and increases overall reliability of the accumulator. More particularly, there is a need for a buckle accumulator that provides increased control of the lead edge of a sheet as it is fed from the input rollers to the output rollers.